1. Field of the Invention
The present invention relates to a method and apparatus for welding synthetic resin members, for example, by a high frequency vibration or an ultrasonic vibration. More particularly, the present invention relates to a method and apparatus for welding synthetic resin members by a high frequency vibration or an ultrasonic vibration which can carry out efficient welding irrespective of peripheral temperature conditions in a welding operation for a synthetic resin member in which the welding is repeated in a short time.
2. Description of the Related Art
Conventionally, welding has been carried out by utilizing a high frequency wave or an ultrasonic wave in order to stick a film or tape formed of a synthetic resin to an object or to bond sheets formed of a synthetic resin. For example, JP-B-51-7424 has disclosed that a synthetic resin piece is pressurized and welded to a slide fastener chain by an ultrasonic wave or a high frequency wave, thereby forming a stopper portion.
The pressure welding using the high frequency wave or the ultrasonic wave for forming the stopper portion is to be carried out repetitively in a short cycle in order to efficiently produce a slide fastener in large quantities, and furthermore, is to be performed under proper temperature conditions in order to firmly weld a synthetic resin piece to the slide fastener chain. In this connection, a welding time is less than two seconds and a standby time is one second so that one cycle is ended in approximately three seconds in total.
In order to firmly weld a synthetic resin piece to a slide fastener chain in such a short time, a great thermal energy is to be quickly given by an ultrasonic wave or a high frequency wave to a synthetic resin piece, a fastener element, a fastener tape and so forth. By giving the excessive thermal energy, the synthetic resin piece, the fastener element and the fastener tape are overheated. For this reason, they become fragile and the stopper portion is broken when external force such as bending or pushing is applied after welding or thread cutting is caused on the faster tape. On the other hand, if a thermal energy is applied to be reduced, the welding is carried out insufficiently. Consequently, the stopper portion is separated from the slide fastener chain after the welding. Accordingly, a strict temperature management is required for the welding using the ultrasonic wave or the high frequency wave.
In order to execute the temperature management, according to JP-Y-63-33531, for example, a heater and a temperature detector are provided on a cut-off die for guiding a thermoplastic film and a film is welded by means of an ultrasonic horn to form a stopper portion in such a state that the temperature of the film is held into a predetermined temperature by means of a temperature controller. According to the same publication, the temperature of the cut-off die is controlled so that the film is preheated and a time required for applying an ultrasonic energy is shortened. Consequently, a stopper portion forming step is ended in a short time so that the productivity of a slide fastener can be enhanced, and furthermore, the film can be welded without applying an excessive thermal energy by means of the ultrasonic horn. Consequently, the film and the fastener tape can be prevented from becoming fragile.
As described above however, this kind of welding is carried out repetitively for a long time in a short cycle, Therefore, heating is carried out by the heat of the film and the fastener tape which is generated at time of the welding, and the temperature of the ultrasonic horn a high frequency electrode is gradually raised. Even if heat corresponding to an increase in the temperature is naturally discharged into the atmosphere, the horn and the electrode are cooled insufficiently. Accordingly, an excessive thermal energy is gradually applied to the synthetic resin piece, the fastener element and fastener tape so that they are caused to be fragile.
As described in the JP-Y-63-33531, particularly, in the case in which the heater is provided in the cut-off die, the temperature of the ultrasonic horn is greatly raised and special cooling is not carried out. Therefore, there is brought a situation in which the set value of the controlled temperature of the cut-off die by the temperature controller is to be changed during an operation.
It is an object of the invention to provide a method and apparatus for welding a synthetic resin member by high frequency or ultrasonic heating which can always weld the synthetic resin member at a proper welding temperature without raising the temperature of an ultrasonic horn or a high frequency electrode to a set temperature or more.
The object can be effectively attained by the invention related to a welding method according to first to fourth aspects and the invention related to a welding apparatus according to fifth to ninth aspects. As described in the first aspect, the invention related to the method for welding synthetic resin members by high frequency or ultrasonic heating is mainly characterized by the following steps.
A method for welding synthetic resin embers by high frequency or ultrasonic heating, include the steps of detecting a temperature of a high frequency vibrating portion or an ultrasonic vibrating portion by a temperature detector, cooling one of the high frequency electrodes or either of an ultrasonic horn and an anvil by cooling means when the temperature detected by the temperature detector during a high frequency or ultrasonic vibration exceeds a present temperature range, thereby reducing the temperature rapidly down to the temperature range, stopping an operation of the cooling means when the temperature of the high frequency vibrating portion or the ultrasonic vibrating portion is reduced to the temperature range, and repeating a start and a stop of the cooling means.
The welding method can be suitably carried out by the invention related to the welding apparatus according to the fifth to ninth aspects. As described in the fifth aspect, the invention related to the welding apparatus is mainly characterized by the following structure.
An apparatus for welding synthetic resin members by high frequency or ultrasonic heating comprises a high frequency or ultrasonic vibrator, a high frequency vibrating portion or an ultrasonic vibrating portion which is connected to the vibrator, temperature detecting means provided additionally in the high frequency vibrating portion or the ultrasonic vibrating portion, cooling means for cooling the high frequency electrode or the anvil, and control means for comparing a temperature detected by the temperature detecting means with a set temperature, thereby operating or stopping the cooling means.
A pair of high frequency vibrating portions include upper and lower molds constituted by an electrode connected to the high frequency vibrator or the ultrasonic vibrating portion includes an anvil and an ultrasonic horn connected to the ultrasonic vibrator, and the synthetic resin members to be welded are provided in a lamination state between the upper and lower molds or the ultrasonic horn and the anvil, and the synthetic resin members are welded by pressure. The high frequency vibrator or the ultrasonic vibrator is operated for a predetermined time to weld the synthetic resin members by the internal heating of the synthetic resin members. This operation is repeated continuously. By the repetition of the welding operation, the amount of heat generated during the welding of the synthetic resin members is transferred so that the temperatures of the high frequency electrodes or the ultrasonic horn and the anvil are raised gradually.
At this time, the temperature of the lower mold electrode for supporting the synthetic resin members to be welded in the high frequency electrodes or the ultrasonic horn is always detected by the temperature detecting means, for example. A temperature signal thus detected is sent to the control means to decide whether or not the temperature is present within a preset temperature range. If it is decided that the temperature of the lower mold electrode or the ultrasonic horn is present out of the preset temperature range, a start instruction signal is generated from the control means so that the cooling means starts an operation to positively cool the lower mold electrode or the ultrasonic horn, thereby reducing the temperatures thereof down to the temperature range. When the temperature of the lower mold electrode or the ultrasonic horn enters the temperature range, a stop instruction signal is generated from the control means, thereby stopping the operation of the cooling means.
Thus, when the temperature of the high frequency vibrating portion or the ultrasonic vibrating portion exceeds the predetermined temperature range, the cooling means is operated to positively drop the temperature of the high frequency vibrating portion or the ultrasonic vibrating portion. Consequently, the temperature of the high frequency electrode or the ultrasonic horn (anvil) can be always maintained in a constant range during the operation of the welding apparatus. Thus, the operation for welding the synthetic resin members is always carried out at a proper temperature in a precise time. As a result, a product of high quality can be obtained, and furthermore, a productivity can be enhanced remarkably.
Examples of the cooling means include a cooling jacket provided in the high frequency vibrating portion or the ultrasonic vibrating portion in addition to the spray of cooling air from an air spray nozzle as is defined in a seventh aspect of the invention.
A second aspect of the invention is directed to the method wherein the high frequency vibrating portion or the ultrasonic vibrating portion is preheated to a predetermined temperature which is equal to or lower than the welding temperature of the synthetic resin members by external heating. For the preheating, a sixth aspect of the invention is directed to the apparatus wherein the high frequency vibrating portion or the ultrasonic vibrating portion has preheating means. Preferably, an eighth aspect of the invention is directed to the apparatus wherein an electric heater is employed for the preheating means and is removably attached to the high frequency vibrating portion or the ultrasonic vibrating portion.
By providing the preheating means in the high frequency vibrating portion or the ultrasonic vibrating portion, the temperatures of the synthetic resin members to be welded can be raised previously. Consequently, a high frequency or ultrasonic energy to be applied can be lessened, and furthermore, a welding time can be shortened. Moreover, since the temperature of the vibrating portion can be raised quickly also in a cold district or at time of the starting operation of the apparatus, for example. Therefore, a preparation time can also be shortened at time of the starting operation. In particular, it is preferable that the electric heater should be employed for the preheating means because the temperature is controlled easily. Furthermore, if the electric heater is removably provided in the high frequency vibrating portion or the ultrasonic vibrating portion, the power of the electric heater which is to be applied can be controlled, and furthermore, the amount of heating by the heater can be regulated by adjusting the amount of insertion.
At this time, the preheating temperature is to be set to be lower than the melting temperature of the synthetic resin to be welded. Usually, examples of a synthetic resin material to be used for a slide fastener include polypropylene, polyester, polyamide and polyacetal. In consideration of the melting temperatures of these resins, it is preferable that the preheating temperature should be set to 65 to 90xc2x0 C. as is defined in a third aspect of the invention.
In a fourth aspect of the invention, the field of use of the synthetic resin member is specified. In particular, one cycle of the welding operation is short, and furthermore, is applied to the formation of the stopper portion of the slide fastener in which a large number of repetitions are carried out, and one of the synthetic resins is a slide fastener chain and the other is a film piece for a stopper.
In the apparatus according to a ninth aspect of the invention, furthermore, a fin, a hole or a concavo-convex portion is provided on the surface of the lower electrode of the high frequency vibrating portion or the ultrasonic horn. Since the fin, the hole or the concavo-convex portion is provided on the surface of the lower electrode or the ultrasonic horn, a contact area with a peripheral atmosphere is increased so that a radiation efficiency can be enhanced. In the case in which the hole or the concavo-convex portion is to be formed, particularly, a heat exchange capability for the inside of the body of the lower electrode or the ultrasonic horn can be enhanced.